(a) Field of the Invention
The present invention relates to a method for preparing a cyclic olefin polymer, and more particularly to a method for preparing a cyclic olefin polymer by addition polymerization of a norbornene-based compound containing polar functional groups such as an ester or an acetyl.
(b) Description of the Related Art
Currently, PMMA (polymethylmethacrylate) or PC (polycarbonate) is widely used for a transparent polymer. Although PMMA has good transparency, it has poor dimensional stability due to its high hygroscopicity. Therefore, it is not suitable for material for precision optical devices or displays.
Until now, inorganic substances such as silicon oxide or silicon nitride have been predominantly used for insulation materials. However, with the increasing need of small-sized and highly efficient devices, new high functional materials are required. In this regard, polymers having a low dielectric constant and hygroscopicity, superior adhesion to metal, strength, thermal stability and transparency, and high glass transition temperature (Tg>250° C.) attract a lot of attentions. Such polymers may be used for insulation films of semiconductor devices or TFT-LCDs, polarizer protection films for polaziers, multichip modules, integrated circuits (ICs), printed circuit boards, and molding compounds for electronic devices or optical materials for flat panel displays. Currently, polyimide, BCB (bis-benzocyclobutene), etc. are used as low dielectric materials for electronic devices.
Polyimide has long been used for electronic devices due to its thermal stability, oxidative stability, high glass transition temperature, and superior mechanical properties. However, it involves problems of corrosion due to high hygroscopicity, an increase in dielectric constant, its anisotropic electric property, a need for pre-treatment to reduce reaction with copper wire, its adhesion to metals, etc.
Although BCB has lower hygroscopicity and a lower dielectric constant than polyimide, its adhesion to metal is not good and curing at high temperature is required to obtain desired physical properties. Physical properties of BCB are affected by curing time and temperature.
Cyclic olefin copolymers are known to have low dielectric constants and hygroscopicity due to their low hydrocarbon content. Cyclic monomers can be polymerized by ROMP (ring opening metathesis polymerization), HROMP (ring opening metathesis polymerization followed by hydrogenation), or copolymerization with ethylene and homogeneous polymerization, as shown in the following Scheme 1.

Polymers synthesized by ROMP have poor thermal stability and oxidative stability due to unsaturation of the main chain, and are used as thermoplastic resins or thermosetting resins. Tenny et al. discloses in U.S. Pat. No. 5,011,730 that a thermosetting resin prepared by the above method can be used as a circuit board by reaction injection molding. However, as mentioned above, it has problems of thermal stability, oxidative stability, and low glass transition temperature.
There has been an attempt to stabilize the main chain of the polymer by hydrogenation. Although a polymer prepared by this method has improved oxidative stability, the thermal stability is reduced. In general, hydrogenation increases the glass transition temperature of a ROMP polymer by about 50° C., but because of the ethylene groups located between the cyclic monomers, the glass transition temperature is still low (Metcon 99). Moreover, a cost increase due to increased polymerization steps and weak mechanical properties of the polymer are hindering its commercial use.
From addition co-polymerization with ethylene, a product called Apel was obtained using a homogeneous vanadium catalyst. However, this method has problems of low catalytic activity and generation of excessive oligomers.
A zirconium based metallocene catalyst has been reported to give a polymer having a narrow molecular weight distribution and a large molecular weight (Plastic News, Feb. 27, 1995, p. 24). However, the activity of the catalyst decreases with the increase of cyclic monomer concentration, and the obtained copolymer has a low glass transition temperature (Tg<200° C.). In addition, although the thermal stability increases, mechanical strength is weak and chemical resistance against solvents such as halogenated hydrocarbon solvents is poor.
Gaylord et al. have reported addition polymerization of norbornene in 1977 (Gaylord, N. G.; Deshpande, A. B.; Mandal, B. M.; Martan, M. J. Macromol. Sci.-Chem. 1977, A11(5), 1053-1070). [Pd(C6H5CN)Cl2]2 was used as a catalyst and the yield was 33%. Later, a norbornene polymer was prepared using a [Pd(CH3CN)4][BF4]2 catalyst (Sen, A.; Lai, T.-W. J. Am. Chem. Soc. 1981, 103, 4627-4629).
Kaminsky et al. have reported homogeneous polymerization of norbornene using a zirconium-based metallocene catalyst (Kaminsky, W.; Bark, A.; Drake, I. Stud. Surf. Catal. 1990, 56,425). However, since a polymer obtained by this method is very crystalline and is hardly soluble in organic solvent, and thermal decomposition occurs without showing glass transition temperature, further studies could not be conducted.
Like the above-explained polyimide or BCB, the cyclic polymers also have poor adhesion to metal. For a polymer to be used for electronic devices, it should have good adhesion to a variety of surfaces, such as silicon, silicon oxide, silicon nitride, alumina, copper, aluminum, gold, silver, platinum, titanium, nickel, tantalum, chromium, and other polymers.
The following method has been introduced to increase adhesion of polyimide, BCB, etc. to metal. A substrate is treated with an organic silicon coupling agent having two functional groups such as amino-propyltriethoxysilane or triethoxyvinylsilane. Then, the substrate is reacted with a polymer or polymer precursor. In this reaction, it is believed that the hydrolyzed silyl group reacts with the hydroxy group on the substrate surface to form a covalent bond.
A cyclic polymer can be used for insulating electronic devices, replacing inorganic materials such as silicon oxide or silicon nitride. For a functional polymer to be used for electronic devices, it should have a low dielectric constant and hygroscopicity, superior adhesion to metal, strength, thermal stability and transparency, and a high glass transition temperature (Tg>250° C.).
Such a polymer can be used for insulation films of semiconductor devices or TFT-LCDs. Here, amino groups on the substrate surface react with functional groups of the polymer or polymer precursor to form bridges linking the substrate and the polymer. This technique has been disclosed in U.S. Pat. No. 4,831,172. However, this method is a multi-step process and requires a coupling agent.
Introduction of functional groups to a polymer comprising hydrocarbons is a useful method for the control of chemical and physical properties of the polymer. However, introduction of functional groups is not easy because unshared electron pairs of the functional groups tend to react with active catalytic sites. A polymer obtained by polymerizing cyclic monomers having functional groups has a low molecular weight (U.S. Pat. No. 3,330,815).
In order to overcome this problem, a method of adding the monomers having functional groups at a later step of polymerization (U.S. Pat. No. 5,179,171) has been proposed. However, thermal stability of the polymer has not increased by this method. Also, physical and chemical properties and adhesion to metal did not improve significantly.
As an alternative, a method of reacting functional groups with a base polymer in the presence of a radical initiator has been introduced. However, this method involves problems in that the grafting site of the substituents cannot be controlled and only a small amount of radicals are grafted. The excessive radicals cut the polymers to decrease molecular weight of the polymer. Or, they are not grafted to the base polymer but polymerize with other radicals.
When a polycyclic compound having a silyl group is used for an insulation film, it adheres to metal and by-products such as water or ethanol are produced, which are not completely removed to increase dielectric constant or cause corrosion of another metal.
Polymerization or copolymerization of norbornene having an ester or acetyl group has attracted continuous attentions (Risse, et al., Macromolecules, 1996, Vol. 29, 2755-2763; Risse, et al., Makromol. Chem. 1992, Vol. 193, 2915-2927; Sen, et al., Organometallics 2001, Vol. 20, 2802-2812; Goodall, et al., U.S. Pat. No. 5,705,503; Lipian, et al., WO 00/20472). Risse et al. activated a [(η3-ally)PdCl]2 palladium compound with a cocatalyst such as AgBF4 or AgSbF6, or used a catalyst such as [Pd(RCN)4][BF4]2. Sen, et al. activated [(1,5-cyclooctadiene)(CH3)Pd(Cl)] with a phosphine such as PPh3 and a cocatalyst such as Na+[3,5-(CF3)2C6H3]4B−. U.S. Pat. No. 5,705,503 used a catalyst system similar to that reported by Risse, et al. ([(η3-ally)PdCl]2 was activated with AgBF4 or AgSbF6.).
In addition polymerization or addition copolymerization of norbornene having an ester or acetyl group, excessive catalyst, as much as 1/100 to 1/400 moles of norbornene, has been used. Lipian, et al. reported polymerization of a norbornene-based monomer using a small amount of catalyst (WO 00/20472). However, most of the preferred embodiments refer to polymerization of alkyl norbornene or copolymerization of alkyl norbornene and silyl norbornene. Although Example 117 refers to polymerization of ester norbornene, the initial addition amount of ester norbornene is only 5% of that of butyl norbornene, suggesting that this method is not efficient for polymerization of ester norbornene. Although the content of ester norbornene in the prepared polymer is not presented, it is expected to be very small. Also, polymerization of norbornene having an acetyl group in Example 134 shows only about a 5% polymerization yield, indicating that the catalyst system is inefficient.
In addition, the literature reported by the inventors of WO 00/20472 in 2001 (Sen, et al., Organometallics 2001, Vol. 20, 2802-2812) shows that the polymerization yield of ester norbornene was below 40%, and an excessive amount of catalyst of as much as about 1/400 moles of the amount of the monomer was used.
It is believed that the reason why such a large amount of catalyst should be used is that catalytic activity decreases due to interaction with a polar group of norbornene such as an ester or acetyl group (Sen, et al., Organometallics 2001, Vol. 20, 2802-2812). Specifically, when polymerizing norbornene having an ester or acetyl group, an exo isomer is more stable thermodynamically, but an endo isomer is stabilized kinetically to generate more endo isomers than exo isomers.
This can be explained by interaction of oxygen lone-pair electrons and π-orbital of a diene in a Diels-Alder reaction or by steric interaction of a methyl group and an ester group of diene, as shown in the following Scheme 2 and Scheme 3.


The endo isomer is known to reduce catalytic activity in the subsequent polymerization steps (Risse, et al., Macromolecules, 1996, Vol. 29, 2755-2763; Risse, et al., Makromol. Chem. 1992, Vol. 193, 2915-2927). Therefore, in polymerization of a norbornene monomer having an ester or an acetyl group, it is desirable that more exo isomers exist in the polymerization solution, if possible. Also, a method of introducing a ligand designed to prevent a decrease in polymerization activity in the presence of endo isomers is required.